Sven E. Harnung

Chemistry of the pedosphere

The pedosphere consists of soil and constitutes the interface between the lithosphere, the hydrosphere, and the atmosphere. Instead of attempting a short definition of soil , we shall look at the main disciplines of soil science: edaphology and pedology, both of which were founded in the 19th century. Edaphology deals with the conditions necessary for the growth of plants (Liebig, around 1840), that is, their nutrition, in particular the types of chemical species they consume and produce. Pedology is the study of soil genesis, morphology, and classification (Dokuchaev, 1883). The upper layer of the Earths crust consists of fragments of rocks, mainly silicates, combined with water, air, and organic material. The largest pieces of rock, boulders and cobbles, have sizes ranging from meters to decimeters, whereas small fragments are coarse gravel in the centimeter range, followed in order of decreasing size by fine gravel, sand, silt, and clay (maximum size 4 μm), as shown later in Table 6.3. This heterogeneous, solid material extending from the outer surface, in contact with the atmosphere or ocean, downward to the solid bedrock, is called the regolith. In some cases the regolith results from weathering of bedrock at a given location, but more often it has been transported to a given site; in a few cases there is no regolith. Material at a given site may have been deposited by ice, water, or wind, individually or in combination. The regolith is often stratified; for example, Figure 6.1 shows layers formed by water and air in material deposited by glaciers.

Chemistry and the Environment: Chemistry of the hydrosphere

The atmosphere interacts directly with the lithosphere, hydrosphere, biota, and society. Noble gases given off by radioactive decay in the core and crust have accumulated since the planet formed, with the exception of He, which has escaped to space. The exchange of water between the atmosphere and the oceans and the land is a key component of weather and the planetary heat engine (see Figure 3.3). The biosphere has dramatically changed the atmospheres composition, including oxygen and the majority of trace gases. Human activities, such as agriculture, industry, and transportation, have left a clear mark on the composition and chemistry of the atmosphere. A summary of the gases found in the atmosphere is given in Section 3.3. The state of the atmosphere affects us all. Crop yields depend on climate, rain, and nutrients present in rain, and on trace gases such as ozone and carbon dioxide. There are also direct effects: WHO estimates that between 2.5 and 11% of human deaths are due to exposure to air pollution. The thickness of the ozone layer at midlatitudes has decreased dramatically over the past generation, not to mention the Antarctic ozone hole. Climate change has important implications for the global ecosystem and public.